CN116184549A

CN116184549A - Optical element and light polarization device

Info

Publication number: CN116184549A
Application number: CN202310296589.3A
Authority: CN
Inventors: 佐藤宽; 齐藤之人; 篠田克己
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2018-09-28
Filing date: 2019-08-27
Publication date: 2023-05-30
Also published as: CN112771420A; JP7397954B2; JP2024028817A; JP2023027201A; CN112771420B; JPWO2020066429A1; WO2020066429A1; US20210208316A1; JP7191970B2

Abstract

The optical element includes a plurality of optically anisotropic layers having an in-plane orientation pattern derived from an optical axis of a liquid crystal compound and continuously rotated in at least one direction within one edge plane, the optically anisotropic layers having regions having different lengths from each other in the direction of the optical axis rotated by 180 DEG in one direction, at least one of the plurality of optically anisotropic layers being an oblique optically anisotropic layer having a plurality of bright and dark line pairs derived from the direction of the optical axis in one direction and having regions having different inclination angles from each other with respect to a normal line of an interface of the optically anisotropic layer in a cross-sectional image of a cross-section cut in the thickness direction in one direction observed by a scanning electron microscope.

Description

Optical element and light polarization device

The present application is a divisional application of the invention patent application with the application date of 2019, 8, 27, the application number of 201980063397.X and the name of "optical element and light polarization device".

Technical Field

The present invention relates to an optical element and a light polarization device provided with the same.

Background

Polarized light is utilized in most optical devices or systems, and development of optical elements for controlling reflection, condensation, divergence, and the like of the polarized light is advancing.

Japanese patent application laid-open publication No. 2014-016632 (hereinafter, referred to as patent document 1), japanese patent application laid-open publication No. 2010-525394 (hereinafter, referred to as patent document 2), and the like disclose a polarized light diffraction element formed by aligning a liquid crystal compound pattern having optical anisotropy.

Further, japanese patent application laid-open No. 2016-519327 (hereinafter, referred to as patent document 3) discloses a polarized light conversion system using a geometric phase element having optical anisotropy that varies non-linearly in at least one dimension along the surface. Here, the pattern alignment of the liquid crystal compound is also utilized.

Disclosure of Invention

Technical problem to be solved by the invention

Patent documents

1 and 2 do not disclose techniques for emitting light in directions having different diffraction angles depending on the incident position, and do not disclose similar descriptions.

As a result of studies by the present inventors, it has been revealed that when light is made incident on a layer having optical anisotropy that has a local optical axis direction that varies non-linearly in one dimension, as in patent document 3, the degree of diffraction differs depending on the incidence position. In such an element, when light is incident and emitted at different incident angles depending on the region, the diffraction efficiency in the plane may be different depending on the region, and a region with reduced diffraction efficiency may be generated.

In view of the above, an object of the present invention is to provide an optical element and a light polarizing device that achieve an in-plane diffraction efficiency averaging and improve the average diffraction efficiency.

Means for solving the technical problems

The following means are included in the technique of the present invention.

In an optical element comprising a plurality of optically anisotropic layers in the thickness direction, the optically anisotropic layers having an in-plane alignment pattern derived from the optical axis of a liquid crystal compound which changes while continuously rotating in at least one direction within one edge plane,

the optically anisotropic layer has regions having different lengths from each other in the one direction until the direction of the optical axis is rotated 180 degrees,

at least one of the plurality of optically anisotropic layers is an oblique optically anisotropic layer having a plurality of bright and dark line pairs oriented from the optical axis along the one direction and having regions in which the bright and dark line pairs are inclined at different inclination angles with respect to a normal line of an interface of the optically anisotropic layer, in a cross-sectional image obtained by observing a cross-section cut along the one direction in the thickness direction by a scanning electron microscope.

The optical element according to < 2 > to < 1 > includes two oblique optically anisotropic layers, and in the cross-sectional image, the oblique angles of the bright line and dark line pair in one oblique optically anisotropic layer and the bright line and dark line pair in the other oblique optically anisotropic layer are different from each other in at least a part of the opposite regions of the two oblique optically anisotropic layers.

The optical element according to < 3 > to < 1 > or < 2 > includes two oblique optically anisotropic layers, and in the cross-sectional image, the bright line and dark line pair in one oblique optically anisotropic layer and the bright line and dark line pair in the other oblique optically anisotropic layer are different in tilt direction with respect to the normal line in at least a part of the opposite regions of the two oblique optically anisotropic layers.

The optical element according to any one of < 4 > to < 1 > to < 3 > includes two of the oblique optically anisotropic layers, and in the cross-sectional image, the bright line and dark line pair in one of the oblique optically anisotropic layers and the bright line and dark line pair in the other oblique optically anisotropic layer have the same oblique direction with respect to the normal line in at least a part of the opposing regions of the two oblique optically anisotropic layers.

< 5 > the optical element according to any one of < 1 > to < 4 >, wherein the oblique optically anisotropic layer has a region in which the optical axis is twist-oriented in the thickness direction.

< 6 > the optical element according to any one of < 1 > to < 5 > has a function of diffracting and transmitting incident light.

< 7 > an optical element according to any one of < 1 > to < 5 >, wherein the liquid crystal compound is aligned in cholesteric order in the oblique optically anisotropic layer.

< 8 > the optical element according to < 7 > has a function of diffracting and reflecting incident light.

The optical element according to any one of < 9 > to < 1 > to < 8 > wherein the in-plane orientation pattern of the optically anisotropic layer is a pattern in which a length of the optical axis in the one direction until the direction of the optical axis is rotated 180 ° is gradually changed in the one direction.

The optical element according to any one of < 1 > to < 9 > wherein the in-plane orientation pattern of the optically anisotropic layer is a pattern in which the one direction is radial from the inside toward the outside.

The optical element according to any one of < 1 > to < 10 > has a region having a length of 10 [ mu ] m or less in the in-plane alignment pattern of the optically anisotropic layer, the region being rotated 180 DEG in the one direction with respect to the optical axis.

< 12 > a light polarizing device comprising: a light polarizing element that polarizes light incident thereto; a driving mechanism for driving the light polarization element; and an optical element as defined in any one of < 1 > to < 11 > disposed on a light-emitting side of the light polarizing element.

Effects of the invention

According to the present invention, in the optical element and the light polarizing device, the average diffraction efficiency in the plane can be achieved and the average diffraction efficiency can be improved.

Drawings

Fig. 1 is a plan view schematically showing an orientation pattern of an optical axis of a part of a surface of an optical element according to embodiment 1.

Fig. 2 is a schematic view of a cross-sectional image obtained by a scanning electron microscope with respect to the optical element shown in fig. 1.

Fig. 3 is a diagram schematically showing a liquid crystal alignment pattern in the thickness direction (z direction) and the horizontal direction (x direction) of the optical element shown in fig. 1.

Fig. 4 is a conceptual diagram showing the effect of an optically anisotropic layer having a horizontally rotated alignment pattern.

Fig. 5 is a schematic view of a cross-sectional image of the optical element of embodiment 2, which can be obtained by a scanning electron microscope.

Fig. 6 is a schematic view of a cross-sectional image of the optical element according to embodiment 3, which is obtained by a scanning electron microscope.

Fig. 7 is a schematic cross-sectional view of an optical element according to embodiment 4.

Fig. 8 is a plan view schematically showing an orientation pattern of an optical axis on a surface of an optical element according to a design modification.

Fig. 9 is a diagram conceptually showing an example of an exposure apparatus for exposing an alignment film to form an alignment pattern.

Fig. 10 is a diagram schematically showing an example of a structure of the light polarization device.

Fig. 11 is a view showing a layer structure of the optical element of comparative example 1.

Fig. 12 is a diagram showing the layer structure of the optical element of example 1.

Fig. 13 is a diagram showing the layer structure of the optical element of example 2.

Fig. 14 is a diagram showing the layer structure of the optical element of example 3.

Fig. 15 is a diagram showing the layer structure of the optical element of example 4.

Fig. 16 is a diagram showing the layer structure of the optical element of example 5.

Fig. 17 is a conceptual diagram showing a method of measuring transmitted light intensity.

Fig. 18 is a diagram showing the layer structure of the optical element of comparative example 11.

Fig. 19 is a diagram showing the layer structure of the optical element of example 11.

Fig. 20 is a conceptual diagram showing a method of measuring reflected light intensity.

Detailed Description

Hereinafter, embodiments of the optical element of the present invention will be described with reference to the drawings. In each drawing, the scale of the constituent elements is changed as appropriate from the actual scale for the convenience of visual recognition. In the present specification, a numerical range indicated by "to" means a range including numerical values described before and after "to" as a lower limit value and an upper limit value. In addition, the terms "orthogonal" and "parallel" refer to the strict range of angles ±10°.

[ optical element ]

Fig. 1 is a plan view schematically showing a part of the surface of the optical element 1 according to embodiment 1, and fig. 2 is a schematic view of a cross-sectional image obtained by observing the cross-section of the optical element 1 with a scanning electron microscope (SEM: scanning Electron Microscope). In the following drawings, the one-sided surface of the sheet-like optical element is defined as the xy-plane, and the thickness direction is defined as the z-direction.

The optical element 1 includes two optically

anisotropic layers

10 and 20 stacked in the thickness direction. The optically

anisotropic layers

10, 20 are composed of cured layers of a composition containing a liquid crystal compound. The optical element 1 may have a structure including a support and an alignment film, and an optically anisotropic layer provided on the alignment film. The optical element of the present invention may be provided with a plurality of optically anisotropic layers in the thickness direction, and is not limited to a two-layer structure, and may be provided with three or more layers.

The optically

anisotropic layers

10 and 20 have an in-plane alignment pattern (in-plane liquid crystal alignment pattern) derived from the optical axis 30A of the liquid crystal compound, which changes while continuously rotating in at least one direction a in one edge plane. An in-plane alignment pattern derived from the optical axis 30A of the liquid crystal compound on the surface of the optically anisotropic layer 20 is schematically shown in fig. 1.

The optical axis 30A derived from the liquid crystal compound is a long axis direction (slow axis) of the rod shape in the case of a rod-like liquid crystal compound, and is a direction (fast axis) perpendicular to the disk-like plane in the case of a disk-like liquid crystal compound. In the following description, the optical axis 30A derived from a liquid crystal compound is also referred to as the optical axis 30A of the liquid crystal compound, or simply as the optical axis 30A.

The in-plane alignment pattern in which the optical axis 30A continuously rotates in one direction a is that the angle between the optical axis 30A and the axis a of the liquid crystal compound aligned in one direction a (hereinafter, also referred to as axis a.) is different depending on the position of the axis a direction, and the angle between the optical axis 30A and the axis a along the axis a is different from that of the axis a

To->

Or->

The pattern of gradual changes is oriented and immobilized. In the optically anisotropic layer shown in fig. 1, the optical axis of the liquid crystal compound is parallel to the surface of the optically anisotropic layer, and the partial regions (unit regions) having a constant orientation of the optical axis are disposed in such a manner that the orientation of the optical axis is rotationally varied continuously in one direction between the partial regions arranged in one directionThe orientation pattern is referred to as a horizontal rotation orientation pattern.

The "gradual change in the angle between the optical axis 30A and the axis a" may be a change in the direction of the optical axis every time a predetermined angle is generated between the unit areas, may be a change not at a predetermined angular interval but at uneven angular intervals, or may be a continuous change. However, the angular difference of the optical axis 30A between the unit regions adjacent to each other in the x-direction is preferably 45 ° or less, more preferably 15 ° or less, and further preferably a smaller angle.

In the optical element 1, in such a horizontal rotation alignment pattern of the liquid crystal compound 30, the length (distance) by which the optical axis 30A of the liquid crystal compound 30 is rotated 180 ° is set to the length Λ of one cycle in the horizontal rotation alignment. In other words, the length of one period in the horizontal rotation alignment pattern is an angle from the optical axis 30A of the liquid crystal compound 30 to the axis A

Becomes the following steps

Distance to the end. In the following description, the length Λ of the one period is also referred to as "one period Λ", or simply "period Λ".

The optically

anisotropic layers

10, 20 in the optical element 1 include regions in which the lengths Λ of one period in the axis a direction are different from each other. In the example shown in FIG. 1, in the direction of axis A, the lengths of one period are respectively Λ _A1 、Λ _A2 、Λ _A3 … … (Λ here _A1 ＜Λ _A2 ＜Λ _A3 ) Is a different region A of ₁ 、A ₂ 、A ₃ … …. In this example, the liquid crystal alignment pattern has a period gradually shortened from the right side to the left side of the paper surface, but the optical element of the present invention may have a region of 2 or more periods different from each other in length. However, when applied to a light polarizing device described later, as shown in this example, a liquid crystal alignment pattern in which the length of one period is gradually changed is preferable. Preferably comprises a circumferenceThe period Λ is a region of 10 μm or less.

In addition, the length of one period in the opposed region may deviate from each other among the plurality of optically anisotropic layers, but is preferably uniform within a range of ±10%.

In this structure, a plurality of optically anisotropic layers are formed in the order of forming the 2 nd optically anisotropic layer by coating or the like, on the basis of the first 1 st optically anisotropic layer, whereby the period can be made uniform.

As shown in fig. 1, when the optical axis alignment pattern is observed by an optical microscope in a state in which the optical element 1 including the optically anisotropic layer is sandwiched between 2 polarizers which are orthogonal, the bright portions 42 and the dark portions 44 are alternately observed. The period of the light and dark (i.e., the period of the bright portion or the period of the dark portion) is half of the period Λ of the horizontal rotation orientation pattern of the optical axis.

At least one of the two optically

anisotropic layers

10, 20 is an oblique optically anisotropic layer, and in this example, the 1 st optically anisotropic layer 10 is an oblique optically anisotropic layer. Hereinafter, the 1 st optically anisotropic layer is also referred to as an oblique optically anisotropic layer 10. Here, the oblique optically anisotropic layer is a layer having a plurality of bright lines and dark line pairs (bright-dark lines) oriented from the optical axis in one direction, and having regions in which the bright-dark lines are inclined at different inclination angles from each other with respect to the normal line n of the interface of the layer, in a cross-sectional image (hereinafter, referred to as a cross-sectional SEM image) in which a cross-section cut in the thickness direction in one direction is observed by a scanning electron microscope (SEM: scanning Electron Microscope). The "bright line and dark line derived from the orientation of the optical axis" refers to a bright line and dark line observed according to the alignment state of the liquid crystal compound in the thickness direction of the optically anisotropic layer.

Fig. 2 is a schematic diagram of a cross-sectional image when a cross-section cut in the thickness direction along one direction of optical axis rotation is observed by SEM. As shown in fig. 2, in the cross-sectional image, a plurality of bright line and dark line pairs inclined with respect to the normal line n of the interface of the inclined optically anisotropic layer 10 are alternately present.

The inclination angle of the bright-dark line relative to the normal n of the interface is according to the x directionThe angle of inclination in this case becomes progressively larger in the x-axis direction (alpha ₁ ＜α ₂ ＜α ₃ … …). Here, the inclination angle of the bright and dark line is defined as an angle smaller than an acute angle of 90 ° with respect to the normal line n.

The oblique optically anisotropic layer 10 has, for example, a twisted orientation in the thickness direction in addition to the horizontal rotational orientation, and thus a bright-dark line is observed in the cross-sectional image.

Fig. 3 schematically illustrates a liquid crystal alignment pattern on a cross section of the optical element 1 illustrated in fig. 1 and 2. The liquid crystal compound here is a rod-like liquid crystal compound 30. In fig. 3, the bright and dark lines that can be observed when the cross section is observed by SEM are superimposed.

As shown in fig. 3, the oblique optically anisotropic layer 10 has a liquid crystal alignment pattern in which a rod-like liquid crystal compound 30 (hereinafter, simply referred to as liquid crystal compound 30) is horizontally rotationally aligned in the x-direction and is twist-aligned in the thickness direction.

The "optical axis is twisted and oriented in the thickness direction" refers to a state in which the orientation of the optical axis aligned in the thickness direction from one surface to the other surface of the optically anisotropic layer 10 is changed to be opposite, and is twisted and oriented in one direction and fixed. The distortional properties include right distortional properties and left distortional properties, but may be applied depending on the direction in which diffraction is desired. In addition, the twist of the optical axis in the thickness direction is less than 1 turn, that is, the twist angle is less than 360 °. For example, in the example of fig. 3, the optical axis of the liquid crystal compound 30 is rotated by approximately 140 ° between one surface side and the other surface side in the thickness direction (z direction). The twist angle of the liquid crystal compound 30 in the thickness direction is preferably about 10 ° to 200 °, more preferably about 45 ° to 180 °. In the case of the cholesteric alignment described later, the cholesteric alignment has selective reflectivity of a specific circularly polarized light having a twist angle of 360 ° or more and reflecting a specific wavelength range. In the present specification, "twist orientation" does not include cholesteric orientation, and selective reflectivity is not generated in an optically anisotropic layer having twist orientation.

When the cross section of the oblique optically anisotropic layer having such a liquid crystal alignment pattern was observed by SEM, the bright-dark line shown in fig. 2 was observed. As shown by the overlapping bright and dark lines in fig. 3, the period of the bright and dark lines coincides with the period of the horizontal rotational orientation.

On the other hand, in the cross-sectional image, a plurality of bright and dark lines are alternately present in the 2 nd optically anisotropic layer 20, but the bright and dark lines of the 2 nd optically anisotropic layer 20 do not have an inclination angle along the normal line n of the interface of the optically anisotropic layer 20. In the 2 nd optically anisotropic layer 20, the orientation of the optical axis in the thickness direction is the same.

In the present optical element 1, as shown in fig. 2, the period Λ of the horizontal rotational orientation in the 1 st optically anisotropic layer 10 _A1 、Λ _A2 … … and period Λ of horizontal rotational orientation in the 2 nd optically anisotropic layer 20 _B1 、Λ _B2 … … are uniform in the opposed regions. Namely, Λ _A1 ＝Λ _B1 、Λ _A2 ＝Λ _B2 ……。

The optical element 1 diffracts and transmits the incident light. For example, when incident light L of predetermined circularly polarized light is made _in Incident light L _in The optically anisotropic layer 20 receives optical power and emits light in a curved direction. The refractive power varies depending on the period of the horizontal rotational orientation, and the smaller the period, the larger the diffraction angle can be obtained. When the incident light L of the prescribed circularly polarized light is made to have the same incident angle in the optically

anisotropic layers

10, 20 _in When incident on a region of different period in the horizontal rotation orientation, the light L is emitted from a region of relatively large period _out1 The outgoing light L in the region of relatively small period compared with _out2 The diffraction angle of (2) is larger.

Here, the principle of the optically anisotropic layer having a horizontally rotationally oriented pattern functioning as a transmissive diffraction element will be briefly described with reference to fig. 4.

In addition, when functioning as a transmissive diffraction element, the optically anisotropic layer preferably has an in-plane retardation Re (λ) (=Δn) with respect to the wavelength λ _λ X d) is 0.3λ to 0.7λ. The retardation Re is preferably 0.4λ to 0.6λ, more preferably 0.45λ to 0.55λ, and particularly preferably 0.5λ. Δn _λ At wavelength lambdaThe birefringence, d, of the optically anisotropic layer is the thickness of the optically anisotropic layer. For example, when light of 940nm is assumed to be incident light, the retardation Re with respect to light of 940nm may be in the range of 282nm to 658nm, and particularly preferably 470nm. When having such retardation Re, the optically anisotropic layer functions as a conventional λ/2 plate, i.e., a function of imparting a phase difference of 180 ° (=pi=λ/2) between orthogonal linearly polarized light components of incident light. The retardation is preferably increased as the lambda/2 diffraction efficiency is closer, but the retardation is not limited to the above range.

When the optically anisotropic layer has a retardation of approximately λ/2, a phase difference of λ/2 is imparted to incident light, and the incident light having predetermined circularly polarized light is converted into reverse circularly polarized light and emitted.

Fig. 4 conceptually shows right-handed circularly polarized light P using a wavelength λ as incident light L1 _R The optical anisotropic layer 11 acts on the optical anisotropic layer 11 having a horizontally rotationally oriented pattern. When incident light L1 of right circularly polarized light of wavelength λ is incident on the optically anisotropic layer 11, right circularly polarized light P _R That is, the incident light L1 is converted into left-circularly polarized light P by imparting a phase difference of λ/2 by passing through the optically anisotropic layer 11 _L . The incident light L1 is changed in absolute phase by the optical axis 30A of the liquid crystal compound 30 in each unit region (partial region) in the horizontal rotation alignment pattern. Here, in the optically anisotropic layer, the orientation of the optical axis 30A of the liquid crystal compound 30 changes by rotating along the axis a, and therefore, the amount of change in absolute phase varies depending on the orientation of the optical axis 30A of the liquid crystal compound 30 at the position of the axis a of the optically anisotropic layer 11 where the incident light enters. In the region indicated by a broken line in fig. 4, a case where the amount of change in the absolute phase Q thereof differs according to the x-coordinate is schematically shown.

As shown in fig. 4, an equiphase surface E having an absolute phase of an angle with respect to the surface of the optically anisotropic layer 11 is formed due to the deviation of the absolute phase Q when passing through the optically anisotropic layer 11. Thereby, a bending force is applied to the incident light L1 incident from the normal direction in the direction perpendicular to the equiphase plane E, and the traveling direction of the incident light L1 is thereby increasedA change occurs. I.e. right circularly polarized light P _R I.e. the incident light L1 becomes left circularly polarized light P after passing through the optically anisotropic layer 11 _L And is emitted from the optically anisotropic layer 11 as an emitted light L2 traveling in a direction at a predetermined angle to the normal direction.

In addition, when left circularly polarized light is incident on the optically anisotropic layer 11 as incident light, the incident light is converted into right circularly polarized light in the optically anisotropic layer 11 and undergoes a bending force opposite to the drawing to change the traveling direction. When the rotation direction of the horizontal rotation orientation of the optical axis 30A of the liquid crystal compound 30 is opposite, the refraction direction of the light by the optically anisotropic layer is opposite to the above.

The shorter one period in the in-plane alignment pattern in the optically anisotropic layer can impart a larger bending force to incident light, and thus can increase the diffraction angle.

The wavelength λ of the light diffracted by the optically anisotropic layer 11 may be from ultraviolet to visible light, infrared, or even electromagnetic wave. The larger the wavelength of the incident light, the larger the diffraction angle, and the smaller the wavelength of the incident light, the smaller the diffraction angle, as long as the period is the same. Therefore, the period may be set according to the target wavelength and the desired diffraction angle.

In addition, although the case where the bending force is applied to the light incident from the normal direction has been described above, the same principle is also adopted in which the bending force is applied to the light incident obliquely, and the outgoing light having an outgoing angle different from the incident angle can be obtained.

In the optical element 1 of the present configuration, since the 1 st and 2 nd optically

anisotropic layers

10 and 20 have regions having different periods of the horizontal rotation alignment pattern in the respective planes, light having different emission angles can be emitted with respect to the same incident angle. As in the 2 nd optically anisotropic layer 20, when not twist-oriented in the thickness direction, the diffraction efficiency for light incident in the normal direction is high, but there is a problem that the diffraction efficiency for light incident obliquely is low. On the other hand, in the oblique optically anisotropic layer 10, diffraction efficiency for obliquely incident light can be improved.

The optical element 1 has a laminated structure of two or more optically anisotropic layers, at least one of which is an oblique optically anisotropic layer, and therefore can improve the average diffraction efficiency when incident with an angle of incidence being changed according to the region, and can suppress the difference in the intensity of the emitted light to average the emitted intensity.

In this example, the optically anisotropic layer has a two-layer structure, but may have three or more layers. The oblique optically anisotropic layer may be one layer, but more preferably has two or more layers.

Fig. 5 and 6 show examples of structures of optical elements 2 and 3 according to embodiment 2 and 3, each of which includes two oblique optically anisotropic layers. Fig. 5 and 6 are schematic views of cross-sectional views of the optical elements 2 and 3. As described above, the cross-sectional image is an SEM image in which a cross section cut in the thickness direction in one direction of the horizontal rotational orientation is observed.

As shown in fig. 5, in the cross-sectional image, the oblique directions of the bright-dark lines in one oblique optically anisotropic layer 10 and the bright-dark lines in the other oblique optically anisotropic layer 22 in the two opposing regions thereof may be different from each other with respect to the normal line n. The different tilt directions with respect to the normal line n means that the tilt direction of the bright-dark line of one tilted optically anisotropic layer 10 with respect to the normal line n is the negative side of the x-axis (left side of the paper), and conversely, the tilt direction of the bright-dark line of the other tilted optically anisotropic layer 22 with respect to the normal line n is the positive side of the x-axis (right side of the paper). The angle of inclination of the bright-dark line with respect to the normal n of the two oblique optically anisotropic layers may be the same in the opposite region (α _n ＝β _n ) May also be different (alpha) _n ≠β _n ). When two oblique optically anisotropic layers are provided, the opposing regions in which the oblique directions of the bright and dark lines are oriented differently may be over the entire region or may be a part of the entire region. In the present specification, the opposed region of the two oblique optically anisotropic layers means a region that overlaps when viewed from the thickness direction in the same xy region.

By reversing the distorting properties of the thickness-direction twist orientation of the one oblique optically anisotropic layer 10 and the other oblique optically anisotropic layer 22, the inclination angles of the bright-dark lines with respect to the normal line can be reversed.

As shown in fig. 6, in the cross-sectional image, the oblique directions of the bright-dark lines in one oblique optically anisotropic layer 10 and the bright-dark lines in the other oblique optically anisotropic layer 24 of the opposing regions of the two layers may be the same direction with respect to the normal line n of the interface. Here, however, one of the opposing regions is inclined by an inclination angle α of the bright-dark line in the optically anisotropic layer 10 _n And another tilt angle gamma of the bright and dark lines in the optically anisotropic layer 24 _n Different from each other. When two oblique optically anisotropic layers are provided, the opposing regions having the same oblique directions of the bright-dark lines may be entirely or partially formed.

By making the pitches of the twist orientation in the thickness direction in the one oblique optically anisotropic layer 10 and the other oblique optically anisotropic layer 22 different, the inclination angles of the bright-dark lines with respect to the normal line can be made different from each other. The different pitches of twist means that the thickness of the optical axis is different up to the same twist angle.

In addition, the two oblique optically anisotropic layers provided in one optical element may include both of the opposing regions having the same oblique direction and the opposing regions having different oblique directions.

In the above, the optical element functioning as a transmissive diffraction element was described, but the optical element of the present invention can also function as a reflective diffraction element.

Fig. 7 shows a cross-sectional view of an optical element 5 according to embodiment 4 functioning as a reflective diffraction element. The bright-dark lines in the cross-sectional SEM image are shown superimposed schematically in fig. 7.

The optical element 5 includes two oblique optically

anisotropic layers

12 and 14. Both oblique optically

anisotropic layers

12, 14 are horizontally rotationally oriented and cholesteric oriented in the thickness direction. In the two oblique optically

anisotropic layers

12, 14, the directions of rotation of the optical axes of the horizontal rotational orientations are opposite to each other, and the directions of rotation of the cholesteric orientations are also opposite.

The oblique optically

anisotropic layers

12, 14 have a cholesteric orientation and thus selectively reflect light of only a specific selected wavelength region of specific circularly polarized light. The center wavelength of the light to be selectively reflected is determined by the cholesteric spiral pitch and the film thickness, and which circularly polarized light is reflected is determined by the direction of rotation of the spiral.

Since the liquid crystal alignment pattern has a horizontally rotated alignment and a cholesteric alignment, a bright-dark line having a different tilt angle is observed in a cross-sectional image, as in the above-described embodiment, because the liquid crystal alignment pattern has a tilt angle in the normal direction (see fig. 7).

In the same manner as described above, the orientation pattern of the optical axis 30A in the in-plane direction of the oblique optically

anisotropic layers

12, 14 is horizontally rotated, and therefore functions in the same manner as the optical element 1. That is, the light source functions to bend the incident light in a predetermined direction by changing the absolute phase of the incident light. Therefore, the optical element 5 has both the function of bending the incident light in a direction different from the incident direction and the function of reflecting the light by the cholesteric orientation, and reflects the light at an angle in a predetermined direction with respect to the reflection direction of the specular reflection. Further, since the areas having different periods of the horizontal rotation orientation are provided in the in-plane direction, the light can be reflected at different reflection angles for the same incident angle.

Further, the average diffraction efficiency when the incident angle is changed according to the region can be improved, and the intensity difference of the reflected light can be suppressed.

In the above embodiments, the pattern in which one period of the horizontal rotation orientation is gradually lengthened in the x direction is shown. As the optical element, it is also preferable that the optically anisotropic layer has an in-plane alignment pattern in which one period becomes shorter gradually from the center in one axis direction toward one end and the other end in the plane.

As shown in fig. 8, it is preferable to have an in-plane orientation pattern in which one direction of the horizontal rotation orientation is set to be radial from the inside to the outside. Fig. 8 is a schematic plan view of an optically anisotropic layer of an optical element according to a design modification. In fig. 8, an in-plane alignment pattern is shown according to the optical axis 30A of the liquid crystal compound. The optically anisotropic layer has an in-plane orientation pattern in which regions of the same optical axis orientation are arranged in concentric circles and the orientation of the optical axis 30A changes while continuously rotating, and the in-plane orientation pattern is arranged radially from the center of the optically anisotropic layer 15.

In the optically anisotropic layer 15, the orientation of the optical axis 30A is shown, for example, by arrow a in a plurality of directions from the center of the optically anisotropic layer 15 toward the outside ₁ Indicated by arrow A ₂ Indicated by arrow A ₃ The direction indicated by the direction indicator changes while continuously rotating. The rotational orientations of the optical axes rotating in the respective axial directions are rotationally symmetrical with respect to the center.

When the optical element 1 having the optically anisotropic layer having the in-plane alignment pattern shown in fig. 8 was observed by an optical microscope while being sandwiched between 2 polarizers perpendicular to each other, the bright portion and the dark portion were alternately observed in concentric circles. The period of light and dark (i.e., the period of dark portions or the period of light portions) on the concentric periodic alignment surface is half of the period Λ of the horizontal rotation alignment pattern. The period becomes shorter toward the outside, and therefore the difference between the diameter of the concentric circle and the diameter of the adjacent concentric circle becomes smaller as the diameter of the concentric circle becomes closer to the outside.

The absolute phase of the circularly polarized light incident on the optically anisotropic layer 15 having the in-plane alignment pattern changes in each of the partial regions where the orientation of the optical axis of the liquid crystal compound 30 is different. At this time, the amounts of change in the absolute phases differ depending on the orientation of the optical axis of the liquid crystal compound 30 into which the circularly polarized light is incident.

As described above, the shorter the one period Λ in the liquid crystal alignment pattern, the larger the angle of light refraction with respect to the incident direction. Therefore, by gradually shortening one period Λ in the in-plane alignment pattern from the center of the optically anisotropic layer 15 toward the outer direction of one direction in which the optical axis continuously rotates, the converging force or the diverging force of the light based on the optically anisotropic layer 15 can be further improved.

In addition, conversely, one period Λ in the concentric liquid crystal alignment pattern may be gradually increased from the center of the optically anisotropic layer 15 toward the outer direction of one direction in which the optical axis continuously rotates.

For example, when a light quantity distribution is to be provided for the transmitted light, depending on the application of the optical element, the optical element may have a structure in which, instead of gradually changing one period Λ in one direction continuously rotating toward the optical axis, the optical axis is continuously rotated, and regions in which one period Λ is locally different in one direction continuously rotating.

Next, constituent materials and a forming method provided in the optical element of the present invention will be described.

< optically Anisotropic layer >)

The liquid crystal composition containing a liquid crystal compound for forming an optically anisotropic layer may contain other components such as a leveling agent, an alignment controlling agent, a polymerization initiator, an alignment aid, and the like in addition to the liquid crystal compound. By forming an alignment film on a support and applying and curing a liquid crystal composition on the alignment film, an optically anisotropic layer in which a predetermined liquid crystal alignment pattern composed of a cured layer of the liquid crystal composition is immobilized can be obtained.

Rod-like liquid crystalline compounds

As the rod-like liquid crystal compound, methylimines, azoxydes, cyanobiphenyl, cyanobenzene esters, benzoates, cyclohexane carboxylic acid benzene esters, cyanophenyl cyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, diphenylacetylenes, and alkenylcyclohexyl benzonitriles are preferably used. Not only the low-molecular liquid crystalline molecules described above but also high-molecular liquid crystalline molecules can be used.

More preferably, the rod-like liquid crystal compound is fixedly aligned by polymerization, and as the polymerizable rod-like liquid crystal compound, makromol.chem., volume 190, page 2255 (1989) can be used; advanced Mat erials 5, volume 107 (1993); us patent 4683327 specification, us patent 5622648 specification, us patent 5770107 specification; international publication No. 95/22586, international publication No. 95/24455, international publication No. 97/00600, international publication No. 98/23580, international publication No. 98/52905; japanese patent application laid-open No. 1-272551, japanese patent application laid-open No. 6-016616, japanese patent application laid-open No. 7-110469, japanese patent application laid-open No. 11-080081, japanese patent application laid-open No. 2001-328973, and the like. Further, as the rod-like liquid crystal compound, for example, a compound described in JP-A-11-513019 and JP-A-2007-279688 can be preferably used.

Discotic liquid crystalline compounds

As the discotic liquid crystal compound, for example, a compound described in japanese patent application laid-open No. 2007-108732 and japanese patent application laid-open No. 2010-244038 can be preferably used.

Other ingredients-

Other components such as an orientation control agent, a polymerization initiator, and an orientation aid can be used as commonly known materials. In addition, a chiral agent is added in order to obtain an optically anisotropic layer having a twisted orientation in the thickness direction or an optically anisotropic layer having a cholesteric orientation in the thickness direction.

Chiral agent (optically active compound)

Chiral agents have the function of inducing a helical structure in the cholesteric liquid crystal phase. The chiral agent may be selected according to the purpose, since the twist direction or the helix pitch of the helix induced by the compound is different.

The chiral agent is not particularly limited, and commonly known compounds (for example, handbook of liquid crystal devices, chapter 3, chapter 4 to 3, TN (twisted nematic), chiral agent for STN (Super Twisted Nematic: super twisted nematic), page 199, edited by the Committee 142 of the Japanese society of academy of sciences, described in 1989), isosorbide, and isomannide derivatives, and the like can be used.

Chiral agents typically contain asymmetric carbon atoms, but axially asymmetric compounds or surface asymmetric compounds that do not contain asymmetric carbon atoms can also be used as chiral agents. Examples of the axially asymmetric compound or the surface asymmetric compound include binaphthyl, spiroalkene, p-cycloaralkyl and derivatives thereof. The chiral agent may also have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent can be formed by polymerization reaction of the polymerizable chiral agent and the polymerizable liquid crystal compound. In this embodiment, the polymerizable group of the polymerizable chiral agent is preferably the same type as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably a polymerizable unsaturated group, an epoxy group or an aziridine group, more preferably a polymerizable unsaturated group, and further preferably an ethylenically unsaturated polymerizable group.

The chiral agent may be a liquid crystal compound.

When the chiral agent has a photoisomerization group, it is preferable to apply and orient the chiral agent, since a pattern of a desired reflection wavelength corresponding to the emission wavelength can be formed by irradiation with a photomask such as an active light. The photoisomerization group is preferably an isomerization site of a compound exhibiting photochromic properties, an azo group, an azo oxide group or a cinnamoyl group. As specific compounds, compounds described in Japanese patent application laid-open No. 2002-080478, japanese patent application laid-open No. 2002-080851, japanese patent application laid-open No. 2002-179668, japanese patent application laid-open No. 2002-179669, japanese patent application laid-open No. 2002-179670, japanese patent application laid-open No. 2002-179681, japanese patent application laid-open No. 2002-179682, japanese patent application laid-open No. 2002-338575, japanese patent application laid-open No. 2002-338668, japanese patent application laid-open No. 2003-313189, and Japanese patent application laid-open No. 2003-313292 can be used.

Solvent-

As the solvent of the liquid crystal composition, an organic solvent is preferably used. Examples of the organic solvent include amides (e.g., N-dimethylformamide), sulfoxides (e.g., dimethyl sulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene, hexane), haloalkanes (e.g., chloroform, methylene chloride), esters (e.g., methyl acetate, butyl acetate), ketones (e.g., acetone, methyl ethyl ketone, cyclohexanone), ethers (e.g., tetrahydrofuran, 1, 2-dimethoxyethane). Preferably an alkyl halide or ketone. Two or more organic solvents may be used in combination.

< formation of optically Anisotropic layer >)

The optically anisotropic layer can be formed by, for example, coating a multilayer liquid crystal composition on an alignment film. The multilayer coating is to apply a liquid crystal composition to an alignment film, heat the composition, cool the composition, and then cure the composition with ultraviolet rays to produce a 1 st liquid crystal immobilization layer, and then repeat the process of applying the composition to the liquid crystal immobilization layer by a recoating method, heat the composition in the same manner, cool the composition, and then cure the composition with ultraviolet rays.

< support body >)

The support supports the optically anisotropic layer or the optically anisotropic layer and the alignment film. The support is not an essential component in the optical element. Or may be peeled off after use in forming the optically anisotropic layer.

The support may be any support as long as it can support the optically anisotropic layer, and various sheet-like objects (films, plate-like objects) can be used.

The support is preferably a transparent support, and examples thereof include a polyacrylic resin film such as polymethyl methacrylate, a cellulose resin film such as cellulose triacetate, a cycloolefin polymer film (for example, a product of the trade name "ARTON", japan Synthetic Rubber co., ltd. Product of the trade name "ZEON OR", product of ZEON Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to the flexible film, and may be a non-flexible substrate such as a glass substrate.

The thickness of the support is not limited, and the thickness capable of holding the alignment film and the optically anisotropic layer may be appropriately set according to the application of the optical element, the material forming the support, and the like.

The thickness of the support is preferably 1 to 1000. Mu.m, more preferably 3 to 250. Mu.m, still more preferably 5 to 150. Mu.m.

< alignment film >

In forming the optically anisotropic layer, an alignment film is provided for aligning the liquid crystal compound in a predetermined liquid crystal alignment pattern.

The alignment film can be any of various commonly known alignment films.

Examples of the film include a friction-treated film composed of an organic compound such as a polymer, an oblique vapor-deposited film of an inorganic compound, a film having a micro-groove, and a film of an accumulated LB (Langmuir-Blodget: langmuir-Brookget) film of an organic compound such as ω -ditridecanoic acid, dioctadecyl methyl ammonium chloride, and methyl stearate.

The alignment film based on the rubbing treatment can be formed by rubbing the surface of the polymer layer several times in a prescribed direction with paper or cloth.

As a material used for the alignment film, polyimide is preferably exemplified; polyvinyl alcohol; a polymer having a polymerizable group as described in Japanese patent application laid-open No. 9-152509; materials used for forming an alignment film and the like described in JP-A2005-097377, JP-A2005-099228, and JP-A2005-128503.

In the optical element of the present invention, the alignment film is preferably a so-called photo-alignment film in which the alignment film is formed by irradiating polarized light or unpolarized light with a photo-alignment material. That is, in the optical element of the present invention, as the alignment film, a photo-alignment film formed by coating a photo-alignment material on a support is preferably used.

The light alignment film can be irradiated with polarized light from a vertical direction or an oblique direction, and the light alignment film can be irradiated with unpolarized light from an oblique direction.

Examples of the photo-alignment material used for the photo-alignment film include azo compounds described in Japanese patent application laid-open No. 2006-285197, japanese patent application laid-open No. 2007-076839, japanese patent application laid-open No. 2007-138138, japanese patent application laid-open No. 2007-094071, japanese patent application laid-open No. 2007-121721, japanese patent application laid-open No. 2007-140465, japanese patent application laid-open No. 2007-156439, japanese patent application laid-open No. 2007-133184, japanese patent application laid-open No. 2009-109831, japanese patent application laid-open No. 3883848 and Japanese patent application laid-open No. 4151746; an aromatic ester compound described in Japanese patent application laid-open No. 2002-229039; a maleimide and/or alkenyl-substituted nadic imide compound having a photo-alignment unit described in JP-A2002-265541 and JP-A2002-317013; a photo-crosslinkable silane derivative described in japanese patent No. 4205195 and japanese patent No. 4205198; JP-A2003-520878, JP-A2004-529220 and JP-A4162850 describe photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable esters; and compounds capable of photodimerization, particularly cinnamate compounds, chalcone compounds, coumarin compounds, and the like described in JP-A-9-118717, JP-A-10-506420, JP-A-2003-505561, international publication No. 2010/150748, JP-A-2013-177561, and JP-A-2014-012323 are preferable examples.

Among them, azo compounds, photo-crosslinkable polyimides, photo-crosslinkable polyamides, photo-crosslinkable esters, cinnamate compounds and chalcone compounds are preferably used.

The thickness of the alignment film is not limited, and may be appropriately set according to the material forming the alignment film to obtain a desired alignment function.

The thickness of the alignment film is preferably 0.01 to 5. Mu.m, more preferably 0.05 to 2. Mu.m.

The method of forming the alignment film is not limited, and various generally known methods corresponding to the material for forming the alignment film can be used. As an example, there is a method of forming an alignment pattern by applying an alignment film to a surface of a support, drying the film, and exposing the alignment film to a laser beam.

Fig. 9 conceptually illustrates an example of an exposure apparatus for exposing an alignment film to form an alignment pattern. The exposure apparatus includes a laser light source 81 that emits a laser beam, a beam expander 82 that expands the beam diameter of the laser beam L emitted from the laser light source 81, a λ/2 plate 83 disposed on the optical path of the laser beam L, a lens 84, and a drive stage 86 that is provided with an alignment film 90. The λ/2 plate 83 is mounted on a rotary bayonet, not shown, and functions as a variable polarization rotator.

The beam diameter of the laser beam L emitted from the laser light source 81 is enlarged by the beam expander 82, and adjusted to an arbitrary polarization direction by rotation of the λ/2 plate 83, and condensed on the photo-alignment film by the lens 84, and the drive stage 86 is driven to scan the exposure photo-alignment film to perform patterning. Thus, a patterned alignment film having a desired pattern can be formed.

In the optical element of the present invention, the alignment film is preferably provided, but is not necessarily a constituent element.

For example, by forming an alignment pattern in the support by a method of rubbing the support, a method of processing the support with a laser beam or the like, an optically anisotropic layer having a horizontally rotated alignment pattern can also be formed.

In the above-described optical elements, the configuration of the incident light having a single wavelength is basically described, but the same effect can be exerted on the incident light having a plurality of wavelengths. As long as the optical element has a structure in which optically anisotropic layers having liquid crystal alignment patterns corresponding to respective wavelengths are laminated, incident light having multiple wavelengths can be used.

[ light polarization device ]

Fig. 10 is a schematic configuration diagram of an example of the light polarization device according to the embodiment.

The light polarization device 130 includes a condenser lens 131, a λ/4 plate 111, a light polarization element 132, and an optical element 120 according to an embodiment of the present invention from the upstream side in the traveling direction of light (light beam). In the following description, the upstream and downstream are referred to as upstream and downstream in the traveling direction of light.

The condenser lens 131 is a commonly known condenser lens, and is provided to allow light (light flux) from a light source (not shown) to enter the light polarizing element 132 in a slightly condensed state. The condenser lens 131 is preferably provided, and is not an essential constituent. However, by providing the condenser lens 131, the light (light flux) emitted from the light polarization device 130 can be converted into appropriate parallel light, and the straightness can be improved.

Further, not limited to the condenser lens 131, any commonly known condenser element capable of condensing light (light flux) may be used.

The λ/4 plate 111 is a generally known λ/4 plate (1/4 phase difference plate) that converts linearly polarized light emitted from a light source to circularly polarized light. As the λ/4 plate 111, a commonly known λ/4 plate can be used without limitation. Thus, the λ/4 plate 111 may be derived from a polymer or from a liquid crystal. In addition, the λ/4 plate 111 can be configured between the MEMS (Micro Electro Mechanical System: microelectromechanical system) light polarizing element 132 and the optical element 120. However, in terms of enabling miniaturization of the λ/4 plate 111, etc., it is preferable to be disposed further upstream than the MEMS light polarizing element 132. When circularly polarized light is incident, the λ/4 plate 111 may not be provided in the light polarizing device 130 using the MEMS light polarizing element 132.

The light polarizing element 132 is a MEMS light polarizing element that scans light in two dimensions. The MEMS light polarizing element is not particularly limited, and a generally known MEMS light polarizing element (MEMS (light) scanner, MEMS light polarizer, MEMS mirror, DMD (Digital Micromirror Device: digital microscopy device)) in which light is polarized (polarization scanning) by swinging a mirror (mirror) using a piezoelectric actuator or the like can be appropriately used, such as the MEMS light polarizing element described in japanese patent application laid-open No. 2012-208352, the MEMS light polarizing element described in japanese patent application laid-open No. 2014-134642, or the MEMS light polarizing element described in japanese patent application laid-open No. 2015-022064.

A driving device 134 for rotationally driving the mirror is connected to the light polarizing element 132. The driving device 134 may be a commonly known device corresponding to the structure of the MEMS light polarizing element 132.

The optical element 120 includes two optically anisotropic layers shown in fig. 8, and the optically anisotropic layers have liquid crystal alignment patterns in planes in which the optical axis is horizontally rotated and aligned along an axis radially provided from the center and the period thereof becomes smaller as the period thereof becomes closer to the outside. As shown in fig. 10, the period Λ from the center region of the optical element 120 ₁ The period becomes smaller as the outside is more outward (Λ ₁ ＞Λ ₂ ＞Λ ₃ ＞Λ ₄ … …). Here, one optical anisotropic layer 121 is an oblique optical anisotropic layer, and the other optical anisotropic layer 122 is an optical anisotropic layer having no twist in the thickness direction and the same pattern in the thickness direction. The optical element 120 is configured to have a center coincident with the center of polarization of the light polarizing element 132. The inclination angle of the bright-dark line with respect to the normal line in the cross-section SE M image of the optical element 120 becomes larger toward the center and smaller toward the outside.

In the light polarization device 130, light having the polarization P with respect to the output surface 120b of the optical element 120, which is emitted from a light source not shown, is slightly condensed by the condenser lens 131, and then is converted into, for example, right-circularly polarized light by the λ/4 plate 111.

The light converted into circular polarization by the λ/4 plate 111 is polarized by the MEMS light polarizing element 132 and is incident on the incident surface 120a of the optical element 120. Light incident on the optical element 120 is diffracted and emitted from the light-emitting surface 120b of the optical element 120, that is, from the light-polarizing device 130.

The center of the optical element 120 is arranged to coincide with the center of polarization of the light polarizing element 132, and thus light scanned by the light polarizing element 132 is incident at a larger incident angle with respect to one face of the optical element 120 with being away from the center of the one face thereof. The period of the horizontal rotation orientation is configured to be shorter as it goes away from the center, and the bending force is stronger as it goes to the outside. Therefore, the optical element 120 transmits light that is vertically incident almost without generating bending force, and is bent and emitted more toward the outside of the optical element 120. By horizontally rotating the optically

anisotropic layers

121 and 122, polarized light to which a bending force is applied from the center toward the outside is made incident on the optical element 120 as incident light, whereby a scanning angle θmaxout larger than the scanning angle θmax of the light polarizing element 132 can be obtained.

Here, when the incident angle of light to the incident surface 120a of the optical element 120 is θ1, the refractive index of the medium on the incident side is n1, the exit angle of light emitted from the exit surface 120b of the optical element 120 is θ2, the refractive index of the medium on the exit side is n2, the wavelength of light is λ, the periodic structure pitch of the liquid crystal diffraction element is Λ, and the diffraction order is m, the relationship between these values can be established by the following equation (1).

n1·sinθ1-n2·sinθ2＝m·λ/Λ(1)

As described above, by changing the period Λ of the horizontal rotation orientation pattern in the optically anisotropic layer of the optical element 120, the angle of the outgoing light from the optical element 120 can be changed.

Considering the snell's law, the angle at which air is finally emitted can reach an absolute value of about 80 °, and therefore the emission angle can be enlarged to a very large angle. Further, by continuously changing the period of the horizontal rotation orientation pattern in the optically anisotropic layer of the optical element 120 in the plane, light can be continuously emitted in an arbitrary direction.

As is clear from the above description, the light polarization device of the present invention can perform light scanning at a scanning angle wider than the scanning angle (viewing angle) of the light polarization element. In fig. 10, a case is shown in which the scanning angle in the x direction is wide, but the horizontal rotation orientation pattern is arranged radially, so that the scanning angle can be enlarged in the y direction on the same principle. Therefore, by diffracting and scanning the polarized light (scanning light) from the light polarizing element 132 by the optical element 120, the scanning range can be greatly enlarged as compared with the scanning range in which two-dimensional scanning can be performed by the light polarizing element 132.

Even in the case where the optical element 120 applied to such a light polarizing device 130 does not have the oblique optically anisotropic layer 121, an effect of expanding the scanning angle can be obtained. However, when an optical element having only the optically anisotropic layer 122 without the oblique optically anisotropic layer 121 is applied, there is a problem in that a large difference occurs in diffraction efficiency in the vicinity of the center where the incident angle is small and in the region of the outer peripheral portion where the incident angle is large and the diffraction angle becomes large, and the diffraction efficiency as a whole (average diffraction efficiency) is low. By providing the oblique optically anisotropic layer 121, the diffraction efficiency of the element outer peripheral portion having a large incident angle can be improved, and the difference in diffraction efficiency due to the incident position and the incident angle can be suppressed, so that the variation in the light quantity of the emitted light can be suppressed. Further, by providing two or more optically anisotropic layers, the average diffraction efficiency can be improved.

In the light polarization device, the optical element 120 is not limited to the above, and for example, an optical element having an optically anisotropic layer with a horizontally rotating alignment pattern whose period gradually decreases from one side to the other side in the x-axis direction as shown in fig. 1 may be used. Further, an optical element having a horizontally-rotated alignment pattern whose period gradually decreases from the center of the element toward the outside in the x-axis direction and an optically anisotropic layer whose rotation directions of the optical axes are opposite across the horizontally-rotated alignment pattern on both sides of the center may be used.

Examples

The features of the present invention will be further specifically described below by way of examples. The materials, reagents, amounts used, amounts of materials, ratios, treatment contents, treatment sequences, and the like shown in the following examples can be appropriately changed within the scope not departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited to the specific examples shown below. In the following examples and comparative examples, it is assumed that a liquid crystal alignment pattern was designed using an infrared light having a target wavelength of 940nm as incident light.

Comparative example 1

An optical element having a non-oblique optically anisotropic layer 211 with a bright-dark line that is not oblique in a cross-sectional SEM image as a 1 st optically anisotropic layer was produced as comparative example 1 (see fig. 11).

< fabrication of optical element >)

(formation of alignment film)

The following coating liquid for forming an alignment film was applied on the glass substrate by spin coating. The support on which the coating film of the coating liquid for forming an alignment film was formed was dried on a hot plate at 60 ℃ for 60 seconds, thereby forming an alignment film.

Coating liquid for forming alignment film

Material A for photo-alignment

[ chemical formula 1]

(exposure of alignment film)

An alignment film P-1 having an alignment pattern was formed by exposing the alignment film using an exposure apparatus shown in fig. 9, which performs patterning by scanning the exposure light alignment film while arbitrarily changing the polarization direction of the condensed laser beam. In the exposure apparatus, a laser beam having an emission wavelength (325 nm) is used as the laser beam. Further, the alignment pattern is formed in concentric circles, and one period of the alignment pattern is gradually shortened from the center to the outside.

(formation of the 1 st optically Anisotropic layer)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-1 was prepared.

Composition A-1

Liquid crystal compound L-1

[ chemical formula 2]

Leveling agent T-1

[ chemical formula 3]

The 1 st optically anisotropic layer was formed by coating the multilayer composition A-1 on the alignment film P-1. First, the 1 st layer composition a-1 was applied onto an alignment film, heated, cooled, and then ultraviolet-cured to prepare a liquid crystal immobilization layer, and then the 2 nd layer was repeatedly subjected to the following procedure, wherein the liquid crystal immobilization layer was applied by a recoating method, and similarly heated, cooled, and then ultraviolet-cured.

First, layer 1 was coated with the following composition A-1 on the alignment film P-1, the coating film was heated to 70℃on a hot plate, then cooled to 25℃and then subjected to a high pressure mercury lamp at 300mJ/cm under a nitrogen atmosphere ² The alignment of the liquid crystal compound was immobilized by irradiation of ultraviolet rays having a wavelength of 365 nm. The film thickness of the 1 st liquid crystal layer at this time was 0.2. Mu.m.

The liquid crystal layer was recoated after the 2 nd layer, heated under the same conditions as described above, cooled, and ultraviolet-cured to prepare a liquid crystal immobilization layer. In this way, the recoating was repeated until the total thickness became the desired film thickness, and the 1 st optically anisotropic layer was formed.

Through the above steps, the optical element of comparative example 1 was produced.

Further, the retardation Re (λ) and the film thickness of a liquid crystal immobilization layer (cured layer) obtained by applying the liquid crystal composition A1 to a separately prepared support with an alignment film for retardation measurement, aligning the director of the liquid crystal compound so as to be horizontal to the substrate, and then irradiating ultraviolet light to immobilize the liquid crystal compound were measured, and the complex refractive index Δn of the cured layer of the liquid crystal composition A1 was obtained. Delta n can be calculated by dividing the retardation Re (lambda) by the film thickness _λ . Retardation Re (λ) was measured using an ellipsometer from Woollam company and at a target wavelength, and film thickness was measured using SEM. In the label of Re (λ), λ is the wavelength of incident light. Hereinafter, the wavelength λ of the incident light is 940nm.

Regarding the 1 st optically anisotropic layer, Δn of liquid crystal ₉₄₀ The x thickness=re (940) was finally 470nm, and the periodically oriented surface was confirmed to be concentric circles as shown in fig. 8 by a polarized light microscope. The concentric periodic alignment surface means that the axis of horizontal rotational alignment is arranged in an in-plane alignment pattern radially from the center. In addition, in the horizontally rotated alignment pattern of the 1 st optically anisotropic layer One period is very large in the center (the reciprocal of the period can be considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter toward the outer direction. And, the twist angle in the thickness direction of the 1 st optically anisotropic layer was 0 °. Hereinafter, "Δn" is performed in the same manner unless otherwise specifically noted ₉₄₀ Measurement of x thickness ", etc. In the SEM-based cross-sectional image, a dark line extending along a normal line, which is a vertical direction, with respect to a lower interface (interface with the glass substrate) of the optically anisotropic layer was observed. In the repeated pattern of the bright-dark lines, the period is observed to be shortened from the center toward the outside.

Example 1

As example 1, an optical element was produced that includes two optically anisotropic layers, the 1 st optically anisotropic layer being an oblique optically anisotropic layer 212 in which the bright-dark line is inclined toward the normal line of the interface in the cross-sectional SEM image, and the 2 nd optically anisotropic layer being a non-oblique optically anisotropic layer 211 (see fig. 12).

(formation of the 1 st optically Anisotropic layer)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-2 was prepared.

Composition A-2

Chiral reagent A

[ chemical formula 4]

In the same manner as in comparative example 1 except that the composition A-2 was used, the 1 st optically anisotropic layer was formed on the alignment film P-1.

(formation of optical Anisotropic layer 2)

The 2 nd optically anisotropic layer of example 1 was the same as the 1 st optically anisotropic layer of comparative example 1, using composition a-1, and the 2 nd optically anisotropic layer was formed on the 1 st optically anisotropic layer in the same manner as the 1 st optically anisotropic layer of comparative example 1, to produce an optical element of example 1.

Regarding the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer, Δn of the liquid crystal was confirmed by a polarized light microscope ₉₄₀ The x thickness=re (940) finally becomes 470nm, and becomes a concentric periodic alignment surface as shown in fig. 8. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction. In addition, the 2 nd optically anisotropic layer is formed by coating on the 1 st optically anisotropic layer, and thus the period thereof is the same as that of the 1 st optically anisotropic layer. In the following, the other layers formed on the 1 st optically anisotropic layer by coating are also the same period. Further, the twist angle in the thickness direction of the 1 st optically anisotropic layer was 140 ° right twist. The twist angle in the thickness direction of the 2 nd optically anisotropic layer was 0 °. In the SEM-based cross-sectional image, a bright-dark line inclined with respect to the normal line of the lower interface (interface with the glass substrate) of the optically anisotropic layer was observed in the 1 st optically anisotropic layer, and a bright-dark line extending in the normal direction was observed in the 2 nd optically anisotropic layer. The 1 st optically anisotropic layer is directed outward from the center and the inclination angle of the bright-dark line with respect to the normal line becomes gradually smaller. Regarding the pattern of the bright and dark lines, the period was observed to be shortened from the center to the outside in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer.

Example 2

As example 2, an optical element was produced that includes two optically anisotropic layers, the 1 st optically anisotropic layer being a non-oblique optically anisotropic layer 211 and the 2 nd optically anisotropic layer being an oblique optically anisotropic layer 212 (see fig. 13). That is, example 2 has a structure in which the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer of example 1 are constituted upside down.

An optical element of example 2 was produced in the same manner as in example 1, except that the 1 st optically anisotropic layer was formed using the composition a-1 and the 2 nd optically anisotropic layer was formed using the composition a-2.

Regarding the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer, Δn of the liquid crystal was confirmed by a polarized light microscope ₉₄₀ The x thickness (Re (940)) was finally 470nm, and it was a periodically oriented surface in the form of concentric circles as shown in fig. 8. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction. And, the twist angle in the thickness direction of the 1 st optically anisotropic layer was 0 °. The twist angle in the thickness direction of the 2 nd optically anisotropic layer was a right twist of 140 °. In the SEM-based cross-sectional image, a bright-dark line extending in the normal direction of the lower interface (interface with the glass substrate) of the optically anisotropic layer was observed in the 1 st optically anisotropic layer, and a bright-dark line inclined with respect to the normal was observed in the 2 nd optically anisotropic layer. The 2 nd optically anisotropic layer is directed outward from the center and the inclination angle of the bright-dark line with respect to the normal line becomes gradually smaller. Regarding the pattern of the bright and dark lines, the period was observed to be shortened from the center to the outside in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer.

Comparative example 2

As comparative example 2, an optical element including an oblique optically anisotropic layer 212 having a bright-dark line oblique to the normal line of the interface in the cross-sectional SEM image as the 1 st optically anisotropic layer was produced.

(formation of the 1 st optically Anisotropic layer)

The 1 st optically anisotropic layer of comparative example 2 was the same as the 1 st optically anisotropic layer of example 1, using composition a-2, and the 1 st optically anisotropic layer was formed on the alignment film P-1 in the same manner as the 1 st optically anisotropic layer of example 1, to produce an optical element of comparative example 2. That is, the optical element of comparative example 2 has a structure having only one oblique optically anisotropic layer as the optically anisotropic layer.

Regarding the 1 st optically anisotropic layer, Δn of liquid crystal ₉₄₀ The x thickness=re (940) was finally 470nm, and the periodically oriented surface was confirmed to be concentric circles as shown in fig. 8 by a polarized light microscope. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction. Further, the twist angle in the thickness direction of the 1 st optically anisotropic layer was 140 ° right twist. In the SEM-based cross-sectional image, a bright-dark line inclined with respect to the normal line of the lower interface (interface with the glass substrate) of the optically anisotropic layer was observed in the 1 st optically anisotropic layer. The 1 st optically anisotropic layer is directed outward from the center and the inclination angle of the bright-dark line with respect to the normal line becomes gradually smaller. The pattern of the dark and light lines is observed to be shorter in period from the center toward the outside.

Example 3

As example 3, an optical element was produced which includes two optically anisotropic layers, and the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer were oblique optically anisotropic layers 213 and 214 (see fig. 14) in which the bright-dark line was inclined toward the normal line of the interface in the cross-sectional SEM image. In the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer, the directions of inclination of the bright-dark lines in the cross-sectional SEM images are the same, and the inclination angles are different.

(formation of the 1 st optically Anisotropic layer)

As a liquid crystal composition for forming the 1 st optically anisotropic layer, the following composition A-3 was prepared.

Composition A-3

In the same manner as in example 1 except that the composition A-3 was used, the 1 st optically anisotropic layer was formed on the alignment film P-1.

(formation of optical Anisotropic layer 2)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-4 was prepared.

Composition A-4

An optical element of example 3 was produced by forming the 2 nd optically anisotropic layer on the 1 st optically anisotropic layer in the same manner as in example 1, except that the composition a-4 was used.

Regarding the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer, Δn of the liquid crystal was confirmed by a polarized light microscope ₉₄₀ The x thickness=re (940) finally becomes 470nm, and becomes a concentric periodic alignment surface as shown in fig. 8. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction. The twist angle in the thickness direction of the 1 st optically anisotropic layer was 160 ° right twist. The twist angle in the thickness direction of the 2 nd optically anisotropic layer was 20 ° right twist. The 1 st optically anisotropic layer and the 2 nd optically anisotropic layer have the same twist direction. In the SEM-based cross-sectional image, a bright-dark line inclined with respect to the normal line of the lower interface of the optically anisotropic layer was observed in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer. The angle of inclination of the bright-dark line with respect to the normal line gradually decreases from the center toward the outside, and the bright-dark lines of the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer are the same in the direction of inclination from the normal line. Regarding the pattern of the bright and dark lines, the period was shortened from the center to the outside in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer 。

Example 4

As example 4, an optical element was produced which includes two optically anisotropic layers, and the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer were oblique optically anisotropic layers 215 and 216 (see fig. 15) in which the bright-dark line was inclined toward the normal line of the interface in the cross-sectional SEM image. In the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer, directions in which bright-dark lines in the cross-sectional SEM images are inclined are different.

(formation of the 1 st optically Anisotropic layer)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-5 was prepared.

Composition A-5

In the same manner as in example 1 except that the composition A-5 was used, the 1 st optically anisotropic layer was formed on the alignment film P-1.

(formation of optical Anisotropic layer 2)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-6 was prepared.

Composition A-6

Chiral reagent B

[ chemical formula 5]

An optical element of example 4 was produced by forming the 2 nd optically anisotropic layer on the 1 st optically anisotropic layer in the same manner as in example 1, except that the composition a-6 was used.

Regarding the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer, Δn of the liquid crystal was confirmed by a polarized light microscope ₉₄₀ The x thickness=re (940) finally becomes 470nm, and becomes a concentric periodic alignment surface as shown in fig. 8. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction. The twist angle in the thickness direction of the 1 st optically anisotropic layer was 80 ° right twist. The twist angle in the thickness direction of the 2 nd optically anisotropic layer was left-twist 80 °. The directions of distortions of the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer are opposite. In the SEM-based cross-sectional image, the bright-dark line was inclined with respect to the normal line of the lower interface of the optically anisotropic layer in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer. The angle of inclination of the bright-dark line with respect to the normal line gradually decreases from the center toward the outside, and the bright-dark lines of the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer are opposite from the direction of inclination of the normal line. Regarding the pattern of the bright and dark lines, the period was observed to be shortened from the center to the outside in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer.

Example 5

As example 5, an optical element was produced which includes three optically anisotropic layers, the 1 st optically anisotropic layer and the 3 rd optically anisotropic layer were oblique optically

anisotropic layers

217 and 218 in which the bright-dark line was inclined toward the normal line of the interface in the cross-sectional SEM image, and the 2 nd optically anisotropic layer disposed between the 1 st and 3 rd optically anisotropic layers was a non-oblique optically anisotropic layer 219 (see fig. 16). In the 1 st optically anisotropic layer and the 3 rd optically anisotropic layer, directions in which bright-dark lines in the cross-sectional SEM images are inclined are different.

(formation of the 1 st optically Anisotropic layer)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-7 was prepared.

Composition A-7

In the same manner as in example 1 except that the composition A-7 was used, the 1 st optically anisotropic layer was formed on the alignment film P-1.

(formation of optical Anisotropic layer 2)

A 2 nd optically anisotropic layer was formed on the 1 st optically anisotropic layer in the same manner as the 1 st optically anisotropic layer of comparative example 1, except that the composition a-1 was used and the film thickness was changed.

(formation of optical Anisotropic layer 3)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition a-8 was prepared.

Composition A-8

An optical element of example 5 was produced by forming the 3 rd optically anisotropic layer on the 2 nd optically anisotropic layer in the same manner as in example 1, except that the composition a-8 was used.

In the 1 st optically anisotropic layer and the 3 rd optically anisotropic layer, Δn of liquid crystal ₉₄₀ X thickness=re (940) finally 470nm, Δn in the 2 nd optically anisotropic layer ₉₄₀ The thickness (Re (940)) was 564nm. The periodically oriented surfaces, which were concentric circles as shown in fig. 8, were confirmed by a polarized light microscope. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period was extremely large in the central portion (the reciprocal of the period was regarded as 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, 3.0 μm at a distance of 4.0mm from the center, and the circumferenceThe period becomes progressively shorter in the outward direction. The twist angle in the thickness direction of the 1 st optically anisotropic layer was 130 ° right twist. The twist angle in the thickness direction of the 2 nd optically anisotropic layer was 0 °, and the twist angle in the thickness direction of the 3 rd optically anisotropic layer was left-twist 130 °. The 1 st optically anisotropic layer is opposite to the direction of twist of the 3 rd optically anisotropic layer. In the SEM-based cross-sectional images, a bright-dark line inclined with respect to the normal line of the lower interface of the optically anisotropic layer was observed in the 1 st optically anisotropic layer and the 3 rd optically anisotropic layer, and a bright-dark line extending along the normal line was observed in the 2 nd optically anisotropic layer. In the 1 st and 3 rd optically anisotropic layers, the inclination angle of the bright-dark line with respect to the normal line gradually decreases from the center toward the outside, and the inclination directions of the bright-dark line with respect to the normal line of the 1 st and 3 rd optically anisotropic layers are opposite. In the pattern of the dark line, the 1 st optically anisotropic layer, the 2 nd optically anisotropic layer, and the 3 rd optically anisotropic layer were each observed to have a period shortened from the center toward the outside.

[ evaluation ]

The optical elements of comparative example 1 and examples 1 to 5 function as transmissive diffraction elements. Regarding each optical element, the angle of the transmitted diffracted light with respect to the normal direction of the optical element at the time of light incidence was measured, and the light intensity increase rate with respect to the element of comparative example 1 was evaluated. The specific measurement method is as follows.

First, a laser beam is made incident on a predetermined position on the surface of an optical element at a predetermined incident angle, and transmitted light is projected onto a screen disposed at a distance of 30cm from the normal direction of the optical element, and the angle of transmitted diffracted light is calculated from an image captured by an infrared camera. A laser diode having a wavelength of 940nm was used as the light source.

Next, as shown in fig. 17, a laser beam having a wavelength of 940nm emitted from the laser light source 251 is transmitted through the linear polarizer 252 and the λ/4 plate 254 to obtain light Li of right-handed circular polarization. The light Li is made incident on a predetermined position on the surface of the optical element S at a predetermined incident angle. The light intensity of the transmitted diffracted light Ld diffracted by the optical element S is measured by the photodetector 256. Then, the ratio of the light intensity of the diffracted light Ld to the light intensity of the light Li is obtained, and the relative light intensity value of the diffracted light Ld with respect to the incident light is obtained. Also, the incident angle was changed and the relative light intensity value was found in the same manner. The light intensity increase rate of the example relative to comparative example 1 was evaluated using the average value of the relative light intensity values for different incident angles as the following criterion.

A: the increase rate of the light intensity is more than 20 percent

B: the increase rate of the light intensity is more than 10% and less than 20%

C: the increase rate of the light intensity is more than 5% and less than 10%

D: the increase rate of the light intensity is less than 5%

In the comparison between comparative examples 1 and 2 and examples 1 to 3, the incident angle was 10 ° at a distance of 1.0mm from the center (one cycle of 9.0 μm), the incident angle was 20 ° at a distance of 2.5mm from the center (one cycle of 4.5 μm), and the incident angle was 30 ° at a distance of 4.0mm from the center (one cycle of 3.0 μm).

In comparison between comparative examples 1 and 2 and examples 4 and 5, the incident angle at a distance of 1.0mm from the center (9.0 μm in one cycle) was set to ±10°, the incident angle at a distance of 2.5mm from the center (4.5 μm in one cycle) was set to ±20°, and the incident angle at a distance of 4.0mm from the center (3.0 μm in one cycle) was set to ±30°, and the evaluation was performed.

The results are shown in table 1.

TABLE 1

Examples 1 to 3 were in the range of 10 to 30 ° in incidence angle, while examples 4 and 5 were each in the range of-30 to +30° in incidence angle, and obtained an average diffraction efficiency higher than that of comparative example 1. By combining oblique optically anisotropic layers with opposite bright-dark line tilt angles in cross-section SEM images, diffraction efficiency can be increased over a wider range of incidence angles. In addition, in the optical element of comparative example 2 having only one oblique optically anisotropic layer, the effect of improving the average diffraction efficiency could not be obtained.

Comparative example 11

As comparative example 11, an optical element having a horizontally rotated alignment pattern with a period gradually changed and having a 1 st optically anisotropic layer 221 with cholesteric alignment in the thickness direction was produced (see fig. 18). In fig. 18, a part with respect to showing a cholesteric orientation in a thickness direction is schematically shown.

(formation of the 1 st optically Anisotropic layer)

As a liquid crystal composition for forming an optically anisotropic layer, the following composition C-1 was prepared. The composition C-1 is a liquid crystal composition for selectively reflecting a cholesteric liquid crystal layer having a center wavelength of 940nm and forming a right-handed circularly polarized light.

Composition C-1

/>

An optical element of comparative example 11 was produced in the same manner as in example 1 except that the composition C-1 was used and the film thickness was changed, and the 1 st optically anisotropic layer was formed on the alignment film P-1.

As a result of confirming the cross section of the coating layer by a scanning electron microscope in the 1 st optically anisotropic layer, the cholesteric liquid crystal phase was 8 pitches, and the periodic alignment surface was confirmed to be concentric circles as shown in fig. 8 by a polarized light microscope. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction. In the SEM-based cross-sectional image, the bright-dark line in the 1 st optically anisotropic layer is inclined with respect to the normal line of the lower interface of the optically anisotropic layer. In the 1 st optically anisotropic layer, the inclination angle of the bright and dark lines gradually increases from the center toward the outside. Regarding the pattern of the bright and dark lines of the 1 st optically anisotropic layer, a case where the period becomes shorter from the center toward the outside was observed.

Example 11

As example 11, an optical element having a horizontally rotated alignment pattern with a period gradually changed and having a 1 st optically anisotropic layer 222 and a 2 nd optically anisotropic layer 223 with cholesteric alignment in the thickness direction was produced (see fig. 19). In fig. 19, a part with respect to showing a cholesteric orientation in a thickness direction is schematically shown.

(formation of the 1 st optically Anisotropic layer)

The composition C-1 was used, and the 1 st optically anisotropic layer was formed on the alignment film P-1 in the same manner as in comparative example 11.

As a result of confirming the cross section of the coating layer by a scanning electron microscope in the 1 st optically anisotropic layer, the cholesteric liquid crystal phase was 8 pitches, and the periodically oriented surface, which was concentric (radial) as shown in fig. 8, was confirmed by a polarized light microscope. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction.

(formation of optical Anisotropic layer 2)

As a liquid crystal composition for forming the 2 nd optically anisotropic layer, the following composition C-2 was prepared. The composition C-2 is a liquid crystal composition for selectively reflecting a cholesteric liquid crystal layer having a center wavelength of 940nm and forming a left-handed circularly polarized light.

< composition C-2 >)

In the same manner as in comparative example 11, the 2 nd optically anisotropic layer was formed on the alignment film P-1.

As a result of confirming the cross section of the coating layer by a scanning electron microscope in the 1 st optically anisotropic layer, the cholesteric liquid crystal phase was 8 pitches, and the periodic alignment surface was confirmed to be concentric circles as shown in fig. 8 by a polarized light microscope. In the horizontally rotationally oriented pattern of the 1 st optically anisotropic layer, one period is extremely large in the center (the reciprocal of the period is considered to be 0), 9.0 μm at a distance of 1.0mm from the center, 4.5 μm at a distance of 2.5mm from the center, and 3.0 μm at a distance of 4.0mm from the center, and the period becomes gradually shorter in the outward direction.

The optical element of example 11 was produced by bonding the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer. When the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer are laminated, the lamination is performed so that the continuous rotation directions of the orientation of the optical axis in the liquid crystal alignment pattern are different from each other.

In the SEM-based cross-sectional image, the bright-dark line was inclined with respect to the normal line of the lower interface of the optically anisotropic layer in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer. The tilt angle of the bright-dark line gradually decreases from the center toward the outside, and the tilt directions of the bright-dark lines of the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer with respect to the normal line are the same. Regarding the pattern of the bright and dark lines, the period was observed to be shortened from the center to the outside in both the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer.

[ evaluation ]

The optical elements of comparative example 11 and example 11 function as reflective diffraction elements. For each element, the angle of reflected diffracted light with respect to the normal direction of the optical element at the time of light incidence was measured, and the light intensity increase rate was evaluated. The specific measurement method is as follows.

The laser beam was made incident on a predetermined position on the surface of the optical element at a predetermined incident angle, the reflected light was projected onto a screen placed at a distance of 30cm from the normal direction of the optical element, and the angle of the reflected diffracted light was calculated from an image captured by the infrared camera. A laser diode having a wavelength of 940nm was used as the light source.

Next, as shown in fig. 20, a laser beam having a wavelength of 940nm emitted from the laser light source 251 is transmitted through the linear polarizer 252 to obtain linearly polarized light Lir. The light Lir is made to enter a predetermined position on the surface of the optical element S at a predetermined incident angle. The light intensity of the reflected diffracted light Ldr diffracted by the optical element S is measured by the photodetector 256. Then, the ratio of the light intensity of the diffracted light Ldr to the light intensity of the light Lir is obtained, and the relative light intensity value of the diffracted light Ldr with respect to the incident light is obtained. Also, the incident angle was changed and the relative light intensity value was found in the same manner. Regarding the average value of the relative light intensity values with respect to the different incident angles, the light intensity increase rate of the examples with respect to the comparative examples was evaluated with the following criteria.

A: the increase rate of the light intensity is more than 20 percent

B: the increase rate of the light intensity is more than 10% and less than 20%

C: the increase rate of the light intensity is more than 5% and less than 10%

D: the increase rate of the light intensity is less than 5%

In comparison between comparative example 11 and example 11, the incident angle at a distance of 1.0mm from the center (one cycle of 9.0 μm) was set to 10 °, the incident angle at a distance of 2.5mm from the center (one cycle of 4.5 μm) was set to 20 °, and the incident angle at a distance of 4.0mm from the center (one cycle of 3.0 μm) was set to 30 °.

The results are shown in table 2.

TABLE 2

Example 11 obtained an average diffraction efficiency higher than that of comparative example 11 in the range of 10 to 30 ° of incidence angle.

The disclosures of Japanese patent applications 2018-185584, filed on 28 at 9 and 2018, are incorporated by reference in their entirety into this specification.

All documents, patent applications and technical standards described in this specification are incorporated in this specification by reference to the same extent as if each document, patent application and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An optical element, wherein,

a plurality of optically anisotropic layers having an in-plane alignment pattern which is derived from the optical axis of the liquid crystal compound and changes while continuously rotating in at least one direction in one edge plane,

the plurality of optically anisotropic layers each have regions having lengths different from each other in the one direction until the orientation of the optical axis is rotated 180 degrees,

the plurality of optically anisotropic layers each have a plurality of bright and dark line pairs along the one direction, the bright and dark line pairs originating from the direction of the optical axis, in a cross-sectional image obtained by observing a cross-section cut along the one direction in the thickness direction by a scanning electron microscope,

The 1 st optically anisotropic layer, which is one of the plurality of optically anisotropic layers, is an oblique optically anisotropic layer having, in the cross-sectional image, regions in which the bright and dark line pairs are inclined at different inclination angles from each other with respect to a normal line of an interface of the optically anisotropic layer.

2. The optical element of claim 1, wherein,

the plurality of optically anisotropic layers includes the 1 st optically anisotropic layer and the 2 nd optically anisotropic layer,

the optical anisotropic layer 1 has a region in which the tilt angles of the bright and dark line pairs in the optical anisotropic layer 1 and the tilt angles of the bright and dark line pairs in the optical anisotropic layer 2 are different from each other.

3. The optical element of claim 1, wherein,

the optical anisotropic layer 1 has a region in which the tilt direction of the bright line and dark line pair with respect to the normal line in the optical anisotropic layer 1 is different from the tilt direction of the bright line and dark line pair with respect to the normal line in the optical anisotropic layer 2.

4. The optical element of claim 1, wherein,

the plurality of optically anisotropic layers sequentially comprising the 1 st optically anisotropic layer, the 2 nd optically anisotropic layer and the 3 rd optically anisotropic layer,

the 3 rd optically anisotropic layer has regions in which the bright line and the dark line pairs are inclined at different inclination angles from each other with respect to a normal line of an interface of the optically anisotropic layer.

5. The optical element of claim 1, wherein,

the optical anisotropic layer 1 has a region in which the tilt angles of the bright and dark line pairs in the optical anisotropic layer 1 and the tilt angles of the bright and dark line pairs in the optical anisotropic layer 2 are different from each other, and the tilt angles of the bright and dark line pairs in the optical anisotropic layer 2 and the tilt angles of the bright and dark line pairs in the optical anisotropic layer 3 are different from each other.

6. The optical element of claim 1, wherein,

the oblique optically anisotropic layer has a region in which the optical axis is twist-oriented in a thickness direction.

7. The optical element according to claim 1, wherein the optical element has a function of diffracting and transmitting incident light.

8. The optical element of claim 1, wherein,

in the oblique optically anisotropic layer, the liquid crystal compound undergoes cholesteric alignment.

9. The optical element of claim 1, wherein,

the optical element has a function of diffracting and reflecting incident light.

10. The optical element of claim 1, wherein,

the in-plane orientation pattern of each of the plurality of optically anisotropic layers is a pattern in which a length of the optical axis in the one direction until the direction of the optical axis is rotated by 180 ° is gradually changed in the one direction.

11. The optical element of claim 1, wherein,

the in-plane orientation pattern of each of the plurality of optically anisotropic layers is a pattern such that the one direction is radial from the inside toward the outside.

12. The optical element of claim 1, wherein,

in the in-plane alignment pattern of each of the plurality of optically anisotropic layers, a region having a length of 10 μm or less is provided until the orientation of the optical axis in the one direction is rotated by 180 °.

13. A light polarization device is provided with:

a light polarizing element that polarizes and emits incident light;

a driving mechanism that drives the light polarizing element; a kind of electronic device with high-pressure air-conditioning system

The optical element according to any one of claims 1 to 12, which is disposed on a light-emitting side of the light polarizing element.